1. Field of the Invention
This invention relates to an electrophoresis apparatus used for separation, analysis or the like of a substance having an electrically dissociated group in a solution, like protein or nucleic acid, on the basis of a difference in the electric charge and molecular weight of the particles.
2. Description of the Prior Art
There has heretofore been known an operation of electrophoresis by which separation of a substance by utilizing migration of charged molecules or particles of protein, nucleic acid, their decomposition product, or the like, is effected in a sheet-like supporting medium such as a gel membrane or a filter paper impregnated with a buffer solution under the effect of an electric field. The electrophoresis is utilized particularly for separation and fixation of the high molecular weight substances of the living body as mentioned above.
Particularly, in the genetic engineering which has attracted attention in recent years, the electrophoresis operation is indispensable for determining base arrangement in the molecule of nucleic acid such as DNA by utilizing autoradiography. In general, the electrophoresis operation for this purpose includes the step of subjecting a series of mixtures of base-specific reaction products of DNA or DNA fragments provided with a radioactive label to migration in the electric field within an electrophoresis supporting medium whereby the mixtures migrate parallel each other in the direction of the electric field. The migration pattern of multiple rows obtained after the migration (a group of zones formed by electrophoresis on the supporting medium) is recorded as an autoradiograph, and then the base arrangement is determined by comparing positions of the zones in the respective rows with each other. The comparison is carried out based on the electrophoresis principle that base-specific reaction products having equal molecular weights migrate to equal distance if the electrophoresis is started from the same line.
In general, filter paper, a membrane filter, a starch gel membrane, a polyacrylamide gel membrane or the like is used as the electrophoresis supporting medium in the form of a sheet having a uniform thickness. In the case where a gel membrane such as a starch gel membrane or a polyacrylamide gel membrane is used, the liquid for gel preparation has heretofore been introduced into a mold constituted by disposing a supporting frame (spacer) around a flat supporting member formed of a non-conductive material such as a glass plate, and gelled for use as the gel membrane, after the upper surface is enclosed by a different supporting member if necessary. However, this method of forming gel membrane is very troublesome as it requires complicated operations prior to the electrophoresis operation.
Accordingly, as disclosed in, for example, Japanese Unexamined Patent Publication No. 59(1984)-126237, the applicant proposed an electrophoresis sheet which requires no troublesome operations of gel preparation and is easy to use. The proposed electrophoresis sheet comprises two sheet members formed of a non-conductive organic polymer film and disposed to stand facing each other, spacers having predetermined thicknesses disposed at both edge portions between the two sheet members, and an electrophoresis gel membrane enclosed between the two sheet members in a uniform thickness. With the proposed electrophoresis sheet, since the gel membrane can be supplied in the form disposed between the two polymer films, the operators can purchase the electrophoresis sheets and easily conduct the electrophoresis operation.
The aforesaid electrophoresis sheet is used, as in the conventional method, in the arrangement so that the gel membrane extends vertically. Therefore, using said electrophoresis sheet, an electrophoresis apparatus provided with a pair of flat plate like supporting members (formed of glass plates, ceramic plates or the like) for supporting the flexible electrophoresis sheet in the form standing erect by sandwiching the sheet from both surfaces thereof is used. Electrophoresis is conducted by applying a gradient in potential in the vertical direction via a buffer solution according to the known method.
However, it was found that, in the case where the electrophoresis sheet is supported by being sandwiched between the flat plate-like supporting members, the migration pattern is distorted even by very small dust or the like which may present between the electrophoresis sheet and the rigid supporting members. Specifically, when the electrophoresis sheet is supported as mentioned above, the gel membrane at the portion where the dust or the like is pushed against the polymer films is distorted together with the polymer film, and the thickness of the gel membrane varries at said portion. Therefore, the migration speed of charged substances under electrophoresis becomes uneven while they pass through the portion where the thickness of the gel membrane is uneven. As a result, distortion of migration pattern such as oblique, bend or zigzag distortion arises. If the migration pattern is distorted, the migration pattern cannot be discriminated or the reading accuracy becomes low. In the case of the operation including the procedure of comparing multiple rows of migration pattern as in the operation for determining the base arrangement of DNA or the like, low accuracy of the migration pattern reading results in low reliability of the information obtained on the base sequence in nucleic acid or the like.